Electromagnetic balance



1952 w. c. BROEKHUYSEN 2,623,741

ELECTROMAGNETIC BALANCE Filed June 11, 1946 6 Sheets-Sheet l FIG. 1

RECTIFIER HIGH D EF QP AND FREQUENCY 0.0. AMPLIFIER OSCILLATOR DAMPINGAMPLIFIER AND PHASE SHIFTING TRANSFORMER 29 DISCRiMINATOR 58 o .INVENTOR50 WILLIAM c. BROEKHUYSEN ATTORNEY Dec. 30, 1952 w. c. BROEKHUYSENELECTROMAGNETIC BALANCE Filed June 11, 1946 6 Sheets-Sheet 2 FIG. 2 15479 62 a? 7 92 90 FIG. 3

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g w 2 II} J W w 6 n, 9 0 9 Ml Dec. 30, 1952 w. c. BROEKHUYSENELECTROMAGNETIC BALANCE 6 Sheets-Sheet 55 Filed June 11, 1946 INVENTORWILLIAM c. BROEKHUYSEN B MI? W ATTORNEY Dec. 30, 1952 w, c, BROEKHUYSEN2,623,741

ELECTROMAGNETIC BALANCE Filed June 11, 1946 6 Sheets-Shet 6 INVENTORWILLIAM C. BROEKHUYSEN ATTORNEY Patented Dec. 39, 1952 UNITED STATESPATENT OFFICE ELECTROMAGNETIC BALANCE Application June 11, 1946, SerialNo. 675,894

(Cl. 265-7ii) 14 Claims.

This invention relates to an electromagnetic balance or scale, and moreparticularly a highspeed electrically controlled weighing device whichmay be used in connection with a cigarette making machine in order todetermine with great rapidity the relative weights of cigarettes issuingfrom the cigarette machine, and which is provided with mechanism forclassifying cigarettes in relation to a predetermined standard weightcigarette. The scale is so connected and synchronized with the operationof a cigarette making machine or other suitable source of supply ofcigarettes to be weighed that each cigarette coming from the machine isweighed and directed into its proper weight classification in greatrapidity. Although the mechanism described herein is shown in connectionwith a continuous cigarette making machine, the use of the scale whichforms a part of the invention is not so limited because obviously it canbe used in other capacities.

I-Ieretofore in the manufactureof cigarettes, weighing devices forweighing cigarettes issuing from cigarette machines have been relativelyslow and in most instances it has been necessary to place cigarettes tobe weighed manually on scale pans and remove them therefrom. Thispractice has, therefore, been quite costly and at the same time becauseof the limited nature of tests made, has not given a true picture to themanufacturer of the relative weights of cigarettes being made.

The present invention, therefore, solves this problem by providing anextremely rapid automatic weighing device which in addition to weighingeach cigarette fed to the scale pan has associated therewith mechanismfor discriminating according to weight variations and for diverting orcounting cigarettes of varying weights into several classifications. Forinstance, a predetermined standard weight may be set as twenty-sixcigarettes per ounce, with cigarettes running more than a certainpercentage above and below that figure as high and low weightcigarettes, respectively.

If such classification be decided upon, the mechanism of the presentinvention is so constructed and arranged that all cigarettes above orbelow the predetermined standard will be counted according topredetermined heavy and light values. This arrangement not only makespossible a more exacting control of the operation of a cigar tte machinebut al o makes it possible for a manufacturer to know, merely byreference to the counters, what numbers of cigarettes are above or belowstandard.

It is, therefore, an object of my invention to 2 provide an extremelyrapid weighing and discriminating device which can be used in connectionwith a cigarette machine or the like, and a hopper containing cigarettesor other articles to be weighed and wherein each cigarette or article isweighed before being conveyed to a collecting device where cigarettes orarticles are prepared for the packaging machines.

Other objects of my invention will be set forth in the followingdescription and drawings which illustrate preferred embodiments thereof,it being understood that the above statement of the objects of myinvention is intended generally to explain the same without limiting itin any manner.

With these and other objects not specifically mentioned in view, theinvention consists in certain combinations and constructions which willbe hereinafter fully described, and then set forth in the claimshereunto appended.

Figure 1 is a sectional side elevation, partly diagrammatic, showing apreferred form of the scale and the operating means therefor includingthe discriminator:

Figure 2 is a top plan view of Figure 1:

Figure 3 is a partial end view of Figure 1, with the casing sectionremoved, to disclose the scale mechanism included therein:

Figure 4 is a view showing the wiring diagram of the scale operatingmechanism:

Figure 5 is a View showing the wiring diagram of the discriminatingunit:

Figure 6 is a side elevation, parts broken away, disclosing mechanismfor feeding cigarettes to be weighed to and from the scale:

Figure 7 is a side elevation taken from the rear of Figure 6, partsbroken away, to disclose elements of the timing mechanism: and

Figure 8 is a front view of Figure '7.

As stated above, the purpose of the invention is to provide an apparatusfor rapidly weighing and for rapid automatic recording of weights or forautomatic sorting according to weight, particularly of very lightobjects or materials; such for instance as cigarettes.

The principles of the invention can be applied to the continuousmeasurement and recording of forces due to causes other than gravity,for example: in hydrostatic or aerodynamic tests. Mor specifically, theinvention constitutes a balance with a much shorter natural period ofoscillation and a much higher degree of damping than can be obtained bypurely mechanical means. From what is described herein, it will beevident that the invention teaches a method of suspension for a scalepan or balance which is not affected by dust, corrosion, or wear such asin the case of knife edges and which is substantially frictionless andexerts substantially no return torque. If desired, a spring-supportedfloating base may be provided which eliminates the effect of vibration.The electric circuit forming a part of the operating means for my scalemechanism includes a two-step, self-biased direct-current amplifierwhich I have found in repeated tests to be quite stable in operation.

Referring to the drawings, in Figure 1 there is shown a preferredembodiment of the scale mechanism in which the balance units consist ofa double beam scale designated generally I, the pivots of which, in theform illustrated, consist of fiat springs l2, Hi, 8 85, 94 and W inbending. An armature [5, preferably formed of soft iron is attached tothe scale in a manner described hereinafter and moves vertically betweentwo permanent magnets I8, 25. The distance between the two magnets isadjustable and preferably is so set that the unbalanced pull of themagnets i8, 29 when armature It is not located centrally therebetween,neutralizes the spring tension of the pivot springs IE, it, 84, 85, 94and Si within the limited range of motion of the scale as determined bystops 22, 2d, described more in detail hereinafter.

An insulated, preferably rectangular, and lightweight plate 26 isattached to an insulating strip 27, which in turn is secured to avertical, movable rod 89 which at its top end has secured thereto thescale pan ea Plate 2d is supported by strip 2? above two horizontallypositioned stationary plates 26, 35) connected by conductors [28, E38extending through shielded cables I32, I34 to a high frequencyoscillator 32. Plates 26, 23 and. 39 form two electrical condensers inseries Whose capacity controls the amplitude of high frequencyoscillation. The output of oscillator 32 is rectified and stepped up bya direct current amplifier 34 in order to control the current in amoving coil 36 also attached to the scale (as shown in Figure 1) andmoving up and down in the gap of a sta tionary magnet 38, which may besimilar in construction to magnets used in magnetic loud speakers.

An increase in weight on scale pan d0, which as mentioned above, isattached to the top end of rod 88, increases the capacity of condensers26, 28, 30, and the amplitude of oscillator 32. This causes a change incurrent in coil 36 of such polarity that the change in force exerted bymagnet 38 on coil 36 opposes the change in weight on scale pan 48. Whenprovisions are made to provide sufficient amplification, thisrerangement can be made so sensitive that the movement of scale pan atis limited to a few thousandths of an inch. For best results, scale pan4B is mechanically balanced for the average or standard weight ofarticles to be weighed so that for a "standard weight the current incoil 36 is zero and the current changes in polarity and intensity dependupon the amount of over and underweight of other similar articles beingweighed. It is evident, therefore, that if a large number of articles,such for example, as a succession of cigarettes, is to be weighed, thescale can be mechanically balanced for a predetermined standard weightcigarette, and all cigarettes weighing more or less than thepredetermined standard will cause changes in polarity and greater orlesser changes in intensity of the current in coil 35 depending on theamount of under and over-weight.

From the above it follows that any change in weight is counterbalancedentirely by a corresponding change in force exerted by the mag net 38 oncoil 36. This force is proportional to the product of the fieldstrength, number of turns of wire on coil 38, and current. The first twobeing constant, the change in weight and current are directlyproportional under balanced conditions, and the coil current isindependent of any factors such as slow variations in line voltage, tubecharacteristics, and changes in circuit constants due to heat andatmospheric conditions.

Since the current in balance coil 35 and, therefore, the forces ofmagnet 33 on this coil are substantially proportional to and 180 out ofphase with the vertical displacement of scale I, the balance has astrong tendency to break into mechanical oscillation, and the change inforce can be made large for a very small displacement, the frequency ofoscillation can be made quite high. Therefore, in order to prevent suchoscillation it is necessary to introduce another or :a damping forcewhich is always opposed to the velocity of the scale, or in other words180 out of phase with the velocity of the scale or out of phase with thedisplacement.

A suitable method of providing the desired damping force is by makingthe form 31 on which coil 36 is wound, out of copper or aluminum. Anymotion of form 31 in the gap of magnet 38 in duces a current in form 31,which current opposes the motion of the scale. This force is by itselfinsuficient, however, and it is necessary to introduce a currentcomponent in coil 36 (or a similarly arranged coil) which is 90 out ofphase with the displacement of the scale, and is zero when scale I is atrest. This can be effected by using a damping amplifier and phaseshifting transformer, designated generally at '29, described more indetail hereinafter. The total damping of the scale can be made highenough so that after any disturbance, such as the arrival and removal ofan article from scale pan 30, scale I will return to a steady balancedposition without overshoot in a minimum length of time, or in otherwords, a critical damping is provided.

The voltage across coil 36 is stepped up by a second direct currentamplifier 42 which charges a condenser 44 through one side of adouble-pole, double-throw set of contacts 46 on a transfer relay 48. Ameter or nul-indicator 5%) may also be connected to amplifier 42 forvisual indication of the weight of articles passing to and from thescale pan 40 and adjustment of the zero point. As soon as the scalecomes to rest and condenser 44 is charged in accordance with the weighton scale pan 4!), the coil of transfer relay i8 is energized through acam operated switch 52. Switch 52, which is provided with a contact M,is normally biased toward contact 56 by a spring 58 mounted on timerhousing 60 fixed to a hub 52 secured to bracket E4 attached to the frameof the machine. Contact 55 is mounted on an adjustable support 66 inorder that it may be located in proper timing adjustment relative tocontact 5Q. A cam 68 Wed to shaft iii separates contacts 54, 55 andbreaks the circuit every time an article leaves the scale pan '30 orarticle supporting portion of scale 1.

Breaking the circuit in this manner at predetermined timed intervals inthe operation of the scale, disconnects condenser 54 from amplifier c2and connects it to a discriminator unit designated generally '52 whichoperates one out of a series of electromagnets i l in accordance withthe polarity and quantity of the charge on condenser s4. ElectromagnetsM may operate counting or tabulating units or sorting apparatus. In thepresent embodiment, since the scale and its operating means areillustrated in operative association with cigarette feeding mechanism,the electromagnets i i are operative to record weight variations incigarettes being weighed in accordance with the weight characteristicsdeveloped in a succession of cigarettes passing to and from scale pan45].

The use of condenser fi l and transfer relay t8 has the advantage thatwhile condenser 4 operates the discriminator unit 12 and oneelectromagnet M, an article on the article support or scale pan t!) ofscale I can be removed, and the next article to be weighed locatedthereon and the scale can be substantially in balance again by the timecondenser 44 is reconnected to amplifier 42.

The construction of a preferred form of scale is shown in Figures 1, 2and 3. Two vertical rods it, 8d are each attached to and maintained inthe desired vertical position by two opposed sets of four leaf springsl2, It forming upper and lower opposed Vs. Adjustably mounted near theupper ends of rods i8, 83 are brackets To one of the brackets is securedone end of a fiat spring t l. To the other bracket is attached a similarspring 8 5. The lower ends of springs 34, G5 are secured to a rigid beamit which, as shown, is mounted in a substantially horizontal plane.Frame plate s2 is secured to the tops of spaced posts 953 which areattached to base plate 92. Base plate 92 which supports the scalemechanism can be attached in any desired manner to any suitable frame orsupports (not shown). Preferably the frame or supports on which thescale is mounted is of a type which can prevent transmission of anyvibration to the scale. Base plate 92 preferably is constructed of anon-conducting material such as Bakelite, hard rubber, Micarta, or othersuitable well-known insulating material. If, however, suitableinsulation is provided for the current carrying parts of the scale, baseplate as may be formed of a conducting material such as iron or steel.

A horizontal leaf spring 8 attached at one end to a projection 95 onbeam '58 and at its other end to post fixed to the underside of plate 82tends to prevent longitudinal movement of beam l5. Spaced depending flatsprings 9'5 are attached to a bracket Q3 mounted on frame plate 522.Springs 97 extend downwardly through an opening in plate 52 and aresecured at their lower ends to a bracket Elli which is fastened byscrews to beam it. In effect, beam it pivots around the intersection ofleaf springs 23 and 9?.

Adjustable stop screws 2'2, 2:3 are mounted in spaced relationship inframe plate 82 and provided with threads in order that by means of nuts23., stop screws 22, 26 can be set at any desired position with respectto the end portions of beam l2 and thereby limit its swing.

disk is mounted. on the lower end of rod it. le t is formed of anon-conducting or insulating material such as Bakelite or like material.conducting metal such aluminum or copper is moun d any suitable manneron disk led. As shown in Figure 1, cylinder 3'! is pressed onto disk il. Coil 343 which is wound about cylinder 3! preferably consists of twoor three layers A cylinder or form 3'2 formed of a high of turns of veryfine enameled wire. The size of wire and number of turns depend upon theimpedance desired. Experience has shown that in the limited spaceavailable between disc H0 and core ll 4 the smallest size of wire andlargest number of turns will still result in a coil of fairly lowimpedance. Cylinder 31 moves freely in the cylindrical gap of permanentmagnet 38, which in the illustrated form, consists of a hollow cylinderHi8, preferably made of Alnico, a well known nickel, cobalt, and ironalloy, or similar material, two soft steel disks H0, H2 and a soft steelcore H4, all suitably secured together and attached in any desiredmanner to plate H5 which is fastened by screws to the underside of baseplate 92 (as shown in Figure 1). A suitable labyrinth seal H8 preventsaccess of dust to the magnet gap. The two leads of coil 36 are connectedto the ends of two of the lower leaf springs l2l2 (as shown in Figures 1and 2).

One end of each of the lower set of springs 12 is adjustably attached,to, but insulated from, rod 18 (as shown in Figure l), the other ends ofthese springs iii are secured to posts H5 formed of conducting materialand attached to the top face of base plate e2. Gne end of each of theupper set of leaf springs I2 is adjustably secured by nuts 8i to rod 18.The other ends of the same springs are secured to posts 33 fastened tothe top face of frame plate 32. One end of each of the upper set ofsprings M is adjustably attached to rod 8% by nuts 8!. The other ends ofthese springs are secured to posts '19 fastened to frame plate 82. Thelower set of leaf springs it are mounted in a similar manner. That is,rod 88 is adjustably supported by one end of each of these springs; theother ends thereof are attached to posts 5 ll secured to base plate 92.

Since it is desired that each article of the succession be weighed inrapid order as it is delivered by a feeding mechanism from a source ofsupply, such as a cigarette machine Or a hopper 268 (shown in Figure 6)when the mechanism forming the present invention is employed forweighing a succession of cigarettes, there is attached to the top end ofscale rod 89 an elongated article supporting plate or scale pan Gil. Theshape and length of plate as is sufficient to allow it to receive andsupport cigarettes delivered thereonto and removed therefrom. Obviouslyany other scale pan could be used dependent upon the use to which themachine is put, or if desired, certain characteristics of an objectbeing tested could be obtained if the object were attached directly torod 88.

A." mentioned hereinabove, armature I6 is attached to rod This armaturepreferably is material having very low hysteresis, such as soft iron,l-lipernic, a high-permeability steei made by Western ElectricCorporation, East Pittsburgh, Pennsylvania, or like material.

Spaced above and below armature are the two U-shaped permanent magnetsit, 28, hereinabove referred to, which magnets are adjustably supportedon a vertical rod Hit passing through an opening 25 in armature it. Thedistance between magnets i3, 23 is adjusted until the pull of themagnets balances the combined tension of all leaf springs if, it, 84,85, 94 and for any position of beam 8 within the set limits of stopscrews 22, 2d, mentioned hereinabove. For best permanent adjustment, theseveral leaf springs preferably are made of a material, such as Elinvar,which contains thirtythree percent nickel with small percentages ofchromium, tungsten, magnesium, silicon and carbon. This material has aconstant modulus of elasticity over a temperature range of 1 to 100 F.as well as a very low coefficient of expansion. Obviously any othersuitable material having similar characteristics can be used and thesame result obtained.

A strip of insulating material 21 clamped to rod 8% and extendingoutwardly therefrom in a substantially horizontal plane has a lightmetal plate 26 secured to its free end (see Figures 1 and 2). Spacedbeneath plate 26 but not in con tact therewith, are two fixed plates 28,36 mounted on posts 3! made of non-conducting or in sulating materialsuch as Bakelite, hard rubber, or the like, supported on block I26.Plates 28, 39 are connected to conductors I28, I30 located in shieldedflexible cables I32, I34 extending upwardly through bores in posts SI.The other ends of conductors I28, I39 lead into high frequencyoscillator 32 (above mentioned).

A relatively small movable weight I36 is adjustably mounted for movementalong rod I 38 in order to adjust the final balance of the scaleaccording to the predetermined standard weight article to be weighed.The ends of rod I38 are supported in brackets 85 secured by screws M2 toboth ends of beam 76. A reference to Figures 1 and 2 will show that rodI38 is substantially parallel with scale beam It. A cover 33 preferablymade of sheet metal, such as steel, surrounds the entire scale assemblyexcept scale pan til. A suitable labyrinth seal It? prevents theentrance of dust around rod 89.

Figures d and 5, show wiring diagrams suitable for operating andcontrolling scale I, in order to rapidly weigh a succession of articlesadvanced to and from scale pan til. Figure 4 discloses oscillator 32,rectifier and amplifier 3t, and amplifier t2, zero indicator 5t andpower supply, energized from power supply lines I68 and IE2. Figure 5shows transfer relay 48, condenser A l, discriminator l2, electromagnetsId, and separate grid and plate power supplies energized from powersupply lines I58, Il'il. Oscillator 32, if desired, may be similar tothe well-known Hartley type. As shown in Figure 4., it uses a triplegrid tube III with high transconductance, like the tube known under thenumber 6867. ta'p I12 of the tuned oscillator coil Ild (T1) is connectedto the positive side of power supply. One end of coil H4 is connected tothe plate of oscillator tube ii I. The opposite end is coupled to thetuned coil i'it (T2) in the grid circuit through the capacity betweenplates 28, 28 and 3G, and condensers E28, lbii in series with theshielded cables H2 and I35. With adjustable condenser I the maximumamount of coupling can be regulated. An initial negative grid bias isobtained with cathode resistor I5I. This reduces the loss in the gridcircuit due to the current in the grid leak. This oscillator circuitgives a smooth control of the amplitude of oscillation from zero tomaximum with an extremely small movement of plate 26, provided not muchload is imposed on the plate circuit. The plate is, therefore, coupledto the grid of an intermediate amplifier tube Hi0 of conventionaldesign. The plate of this tube is coupled to a double-diode tube,designated I82, used as two separate half-wave rectifiers. The outputvoltages of the two sides of tube I62 are of opposite polarities and areconnected to the grids of two power tubes I84 and I86 which form part ofa D. C. bridge circuit. Two arms The center of the bridge consist offixed resistors E88 and I99. The other two arms consist of the plateresistances of the two power tubes I84 and I86, one in series with asmall fixed resistor I92, the other in series with a potentiometer I94of twice the value of resistor I92. Balance coil 36 is connected byleads I52, I54. across the diagonal of this bridge (in series withresistors I96 and I98) so that with the contact arm 28!! ofpotentiometer I94 adjusted to its center, the current in coil 36 is zeroif the plate currents in tubes i8 1 and I86 are the same. The twocathodes of these tubes are connected to ground (the negative side ofpower supply being also connected to ground), through a common cathoderesistor 262. The grid return of tube I86 is connected to the groundside of resistor 262, the grid return of tube I84 to the cathode end.Thus, for zero amplitude of the oscillator the plate current of tube I86will be at its minimum value, and for tube I at its maximum value, andthe current through coil 36 will be a maximum in the direction from I86to I84. For fifty percent output of the oscillator 32 the grids are atthe same potential and the coil current is zero. For maximum oscillatoramplitude the coil current is a maximum in opposite direction. Thecircuit constants can be so chosen that the sum of the two platecurrents and, therefore, the drop across cathode resistor 282 remainsvir tually constant.

As the change in voltage drop across coil 36 and resistors I and I98 fora given change in weight is too small to be used directly to actuatediscriminator I2, the two plates of tubes I8 and I86 are connected tothe two grids of the double triode designated 26 5 which may be of thetype known as 6SN'7. These two triodes are connected in a bridge whichmay be quite similar to tubes I83, I85 and the voltage across thediagonal of this bridge (the plates of the triodes) is used to chargethe transfer condenser. The drop across the common cathode resistor 26%of the two triodes again is constant within the operating range. As thetotal of all plate currents of tubes I85, I86 and 26!; remainspractically constant, there is no feed-back due to the internalimpedance of the power supply, and no tendency to oscillate at lowfrequency. A multi-stage resistance capacity filter 2% attenuates thecycle ripple from the power supply, and also prevents sharp surges dueto mechanical shock, etc., from getting through to the output.

The two plates of tube 253% are also connected to the two controlelectrodes of the electron-ray indicator tube designated 59. For zerooutput voltage, the two shadows of this tube are alike. The zero outputpoint can be shifted over a limited range in relation to the zero coilcurrent point by adjustment of potentiometer E84. This takes care alsoof minor differences between the two triodes of tube 265.

In the circuit, as described so far, the change in grid voltage of tubesI84 and I86 is substantially in phase with any change in oscillatoramplitude and, therefore, with any change in position or thedisplacement of plate 25, and of the scale. As the impedance of coil 36is low compared to resistances of I95 and I98, the current through coil36 is also in "phase with the displacement, which is the ideal conditionfor oscillation of the scale. By shunting resistors I96, I98 withsuitable condensers I97, I99, current changes in coil 36 can be made tolead voltage changes on the grids of tubes I36, I85, and lead thedisplacement of scale I. This acts as a strong damping force and yetdoes not affect the steady value of the current in coil 36.

An even greater damping sheet can be obtained by a circuit additionsimilar to a volume expansion circuit in audio-amplifiers. This involvesanother twin type tube 2l2 which can also be a 6SN'7. One half is usedas a diode, which is coupled to the plate or" the oscillator Ill andrectifies its output. The D. C. output is impressed across the highresistance potentiometer 214. The sliding contact of this potentiometeris coupled to the grid of the second half of tube 212 through acondenser resistor circuit which has a high time constant compared tothe period of oscillation of the scale I. The second half is used as atriode amplifier. The primary of a transformer 2 i 6 with a goodresponse at the frequency of oscillation of the scale is connected inthe plate circuit of this triode. The impedance of the primary should below compared to the triode plate resistance, so that the plate currentis substantially in phase with the grid voltage. The voltage across theprimary and secondary will be 90 ahead of the plate current and,therefore, 90 ahead or the displacement of scale I. The secondary oitransformer 256 is shunted with R. by-pass condenser Zld. The grid oftube I85 is now connected to the secondary of transformer Zid. Since theamplification constant of tube its depends on its grid bias, anymomentary change in output of transformer 2 i6 will cause acorresponding momentary change in output of the tube 89 and in the gridvoltage of tubes i 84, lbs. Thus any change in position of scale willcause a change in the current in coil 35 which has two components, oneof which is permanent if the change in position is permanent and isalways 180 out of phase with the change in position, and a dampingcomponent which is zero when scale l is at rest and is 90 ahead of theother component while scale I is moving. It will be seen that the effectof this additional circuit is very similar to the effect of thecondensers shunted across resistors Hi5, I98. Either or both of thesemethods of damping may be used with or Without the aluminum or coppercylinder inside coil 36.

The discriminator consists essentially of a plurality ofgrid-controlled, gas-filled rectifiers or thyratrons 225; for example,of type 2050 or 2051.

The plates of these tubes are connected to a 1 common supply throughindividual resistors 222. A gas-filled voltage-regulator tube 22%, forexample, a V. R. 105-38 is connected between each plate and ground. Asmall R. F. choke 226 in series with each plate and a R. F. by-passcondenser 228 from each plate to ground prevent oscillation in the platecircuit. A series of solenoids i l for operating counters ill orselective or classifying apparatus (not shown) are connected between theplates of successive tubes.

The grid bias for the thyratrons is obtained from a separate supplyconsisting of a conventional full-wave rectifier 239 and single stagefilter consisting of an iron core choke 23! and a condenser 233,grounded at the positive side, and a voltage regulator tube 232 inseries with resistor 22!. A bleeder circuit consisting of a number ofpotentiometers 235 and resistors 23'! in series is connected to groundthrough a half wave rectifier tube 28:. and to the negative terminal ofthe grid supply through a small iron core choke 235.

Let us assume, in order to explain the action, that the grid bias supplyis 150 volts and that 1G in the illustrated embodiment there are seventhyratrons 22d, numbered 1 to 7, whose grids are connected to taps onthe bleeder circuits as follows; *4, -20, -40, -60, -1G0, 120, and -140,volts.

High resistances are connected in series with each grid. Assume alsothat the thyratrons will fire when their grid bias is zero. After thetransfer relay disconnects the transfer condenser 44 from the balance orscale circuit, it connects the condense 24 between ground and a 80 volttap on the bleeder circuit. Relatively large condensers 2 5:; areconnected between this tap and the -l volt tap and between the 80 andl40 volt taps. If the charge on the transfer condenser was zero, amomentary surge of minus 89 is imposed on the entire bleeder circuitbetween the minus 4 and minus 140 volt taps. This surge is quicklydissipated through the choke 236, but oscillation is prevented by thehalfwave rectifier 23 5. The duration of this surge is so short thatcondensers 244 do not discharge noticeably through the bleeder circuit.Thus thyratron tubes #1, 2, 3 and 4 whose grids are connected to the e,20, 40, 69 volt taps Will fire, but the highest potential reached by thegrid of tube #5 will be 20 volts, so tubes #5, 6 and '7 do not fire. Ifthe charge on the transfer condenser 44 was more than -20 volts, thesurge will be less than (6 and only tubes #1, 2 and 3 will fire, etc.For a charge of more than -76 volts, no tube will For a charge of morethan +20 volts, tubes #1 to 5 will fire. For a charge of more than +66volts, all tubes will fire. It should be noted that whenever one or morethyratrcns fire, their corresponding voltage regulator tubes 224'. areextinguished. The plate current is, so to say, transferred from thevoltage regulator tube to the thyratron, and there is only a moderatechange in load on the power supply.

As the plates or all tubes that fired are at the same potential(approximately +14 volts for the 2051) and also all those that did notfire are at equal potentials (+105 for the VR 105) only oneelec'troinagnet 18 will be energized; that is, the electromagnet betweenthe last tube to fire and the first one not to fire. The last solenoid Mis connected between the plate of the last thyratrcn 229 and the plateof an extra voltage regulator tube 225 which latter is also connected tothe plate supply through resistor 222.

As mentioned hereinabove, the mechanism described can be employed forthe purpose of weighing a succession of articles such as cigarettes andclassify each article as weighed according to a set standard forcigarettes above or below that standard. Each of the seven magnets !4can be connected by suitable means (not shown) to counting or ejectingdevice which will cause cigarettes above and below the predeterminedstandard to be either recorded or ejected as desired. For example, inthe embodiment illustrated, seven grades or classifications ofcigarettes can be determined, such as: E. E. Light, E. Light, Light,Standard, Heavy, E. Heavy and E. E. Heavy, reading from left to right inFigure 5. Applying these principles to the present machine, therefore,the operation of the mechanism can be summarized as follows: For acondenser charge of 20 to +20 volts. the magnet marked Standard" betweentubes #4 and 5 will be energized. For a charge between +20 and +40 theelectromagnet marked Heavy" between tubes #6 and 5 will be energized,etc.

For a charge between 60 and -75 volts, the eleotromagnet marked E. E.Light will be energized. For a charge of more than -76 volts, no magnetis energized. In this way, it can be arranged that no magnet isenergized when there is no object on the scale pan at the instant oftransfer of the condenser.

The cathodes and screen grids of all thyratrons are connected to asingle conductor 246, which is connected to ground through the normallyclosed contact 2&8 of relay 255. The coils of this relay and of transferrelay &8 are connected in series to the plate supply of the thyratrons.A mechanically operated timing contact 52 is connected in the groundlead of these coils. When this contact closes, transfer relay 18 isenergized immediately. The operation of relay 258 is delayed, however,by a large condenser 252 connected across its coil. As a result contact2 58 does not open until the thyratrons have fired, a selected magnethas been energized, and the surge in the grid circuit has died away.When it does open, the plate current in the thyratrons is interruptedand can only be restarted by another surge after contact 2&8 has beenclosed again. This contact is shunted by a small resistor 254 andcondenser 256 to eliminate surges during its opening and closing. Thetiming contact is shunted by a condenser 258 for the same reason.

When the above described mechanism is to be used in grading cigarettes,it is necessary to make certain adjustments in order to classify thecigarettes being weighed according to a predetermined standard, thoseweighing more than standard and those weighing less than standard. Thefirst adjustment made is to place a cigarette of predetermined standardweight on scale pan ii! after which potentiometer N34 is adjusted untilthe two shadows of the indicator tube are alike.

When the timing contact 52 is closed, the Standard" magnet is isenergized momentarily. The scale pan is then emptied and a Heavycigarette is placed on the scale pan ii] and the corresponding gridpotentiometer of the discriminator is adjusted until upon closing of thetiming contact 52 the heavy magnet M is energized. The heavy cigarettejust weighed is then removed from the scale pan and a cigarettecorresponding to the heaviest cigarette to be weighed is placed on scalepan ti! and the grid potentiometer adjusted until upon closing of timingcontact 52 the E. E. heavy magnet Hi is energized. In the same mannerthe weight is decreased according to predetermined lightness ofcigarettes so that cigarettes varying widely from E. E. light to E. E.heavy can be weighed in rapid succession. If each magnet is connected toa counter of any conventional design, it will be evident that ascigarettes are placed in succession on scale pan ii], a count can bemade of varying weights in accordance with the standard set on thepotentiometers 235 varying from E. E. light through standard to E. E.heavy weights.

First, scale pan All is empty, the timing contact 52 is open, thecondenser is connected to the scale and has a high negative charge. Whenan object to be weighed is deposited on the scale, pan 69 moves down animperceptible amount, the current in coil 33 changes to a new valuewhich reestablishes balance, the condenser charge is reduced, and incase of overweight, reversed in polarity. After sufficient time haselapsed for this charge to reach a steady state (perhaps second), thetiming contact closes, the condenser is disconnected from the scalecircuit, and connected to the grid circuit of the discrhninator, one ormore thyratron tubes fire and a corresponding number of V. R. tubes areextinguished, one magnet is energized, contact 248 opens, the thyratrontubes are extinguished, the V. R. tubes relight, the magnet isdeenergized. When this takes place, which again requires second, thefirst objects have been removed from the scale and the second onesdeposited so that a balanced condition is already on the way to bereestablished when the timing contact opens and the condenser isreconnected to the scale circuit.

In Figures 6, 7 and 8, there is shown a suitable mechanism for feedingcigarettes in timed relation to scale pan 29 in order that they may beweighed and classified and passed rapidly to and from scale pan it. Themechanism selected for purposes of illustration consists of a hopper 2%supported by frame members 262. Mounted within the hopper adjacent oneend thereof and spaced above belt 255 which forms the bottom of thehopper, a distance slightly greater than the maximum diameter of acigarette, is a rotary stripper 26d fixed to a shaft 265 suitablysupported by the sides of the hopper 250 for rotary movement. Stripper26 i insures the delivery of cigarettes in single row formation on belt266 in order that they may be guided by belt 265 beneath curved guide267 and a guide 269 spaced therefrom into position to be placed ontoscale pan 45.

Belt 2% is substantially the width of hopper 2% and is supported bydrums 258, 279 fixed to shafts 2'52, El i suitably journalled in sideframe 252. On one end of shaft 265 (Figure 7) is attached a pulley 21 6over which runs a belt 219 also running a pulley 2?? attached to shaft214. A pulley 2718 also attached to shaft 2M has running thereon a belt282 which also runs on a pulley 28E} attached to shaft 284. In thismanner, shafts 255 and 2'54 are driven in proper timed relationship in acounterclockwise direction (as shown in Figure 6) in order to operatethe stripper 26 3 and allow belt 266 to advance a row of cigarettes inrapid succession to weighing position on scale pan dd. A shaft 286supported by brackets 288 attached to side frames 252 is provided ateach end with an arm 2% which at their free ends support a transversebar 292. One of the arms 2% (as shown in Figure 7) is provided with acam follower 2595. A spring 2% attached to a bracket 288 presses againstone of the arms 2933 and urges cam follower 294 into continuousengagement with a earn 2% mounted on shaft 3%. Cam 2% is provided withfour high and four low portions so that during the rotation of the camfor each revolution thereof pusher bar 292 moves back and forth fourtimes to feed cigarettes to be weighed onto a scale pan 4H. Obviouslyany desired number of high and low portions could be provided on cam298.

For the rate of rotation of cam 2528 and the speed of delivery ofcigarettes to and from scale pan d9, experience has shown that a fourloop cam operates satisfactorily. As each cigarette is moved downwardlybetween guides 261, 269, it comes to rest on a platform 352 in front ofbar 292. As shown in Figure 6, three cigarettes are positioned insubstantially horizontal relationship, one cigarette rests upon scalepan 40, another rests in seats provided in the ends of two spaced flatsprings 36 iextending upwardly 13 through slots in the platform cs2.Springs 394 are secured to the undersides of abutments or frames 262 bymeans of screws 3%. Cam shaft 3% is suitably journalled in bracket 3%attached to side frames EH38 forming a part of the feeding mechanism. Adrum ills mounted on shaft 28:3 supported by side frames is providedwith a plurality of spaced flights ti l which are adapted to moveupwardly in a counterclockwise direction (as viewed in Figure 6) inorder to engage the ends of cigarettes resting on scale pan to and movethem from th scale pan upwardly beneath curved guard tit extendingbetween side frames 388 aiiixed thereto by screws Bi'if-l downwardlybetween guide extensions Bit and guide 328 onto belt 322 which runsalong table 32% attached by brackets 328 to side frames 358. In thismanner cigarettes which have been weighed are rapidly removed from thescale and delivered out of the machine. Following the removal of aweighed cigarette from scale ii by a flight 3M, the next cigarette to beweighed is moved from its seat in the ends of springs 3% by a cigarettewhich has moved downwardly between guides 281, 259 into the path ofmovement of pusher bar 292. On the rearward movement of pusher bar 292 acigarette drops into the space between the cigarette on the seat insprings tilt and the face of pusher bar 252 awaiting movement on thenext forward travel of pusher bar 292 onto scale pan til. It will beremembered that magnets 14 are energized in accordance with widegraduations of cigarettes being weighed varying from EE light throughstandard to EE heavy and that counting mechanism can be employed whichwill register all cigarettes passed to and from scale pan 49 so that anaccurate count of the weights of cigarettes can be maintained by certainof the mechanism described herein.

Cam 298 is driven in a clockwise direction by means of a gear 328 formedon a hub of cam 288 secured to shaft 3%, which gear meshes with gear 333on shaft 28 A gear 332 on a stud 334 supported by bracket -liit (Figure8) meshes with gear 336 on shaft 383 journalled in side frames 398. Theother end of shaft 3-33 is provided with a gear Edi! which meshes with agear 362 on shaft "it. By means of gear chains described and pulley 3%by a belt 3% driven from a pulley, a suitable source of power rotationis imparted to the several operated means above described. The design ofthe gear train is such that cigarettes are moved to and from scale panill at any suitable desired rate of speed.

The invention above described may be varied in construction within thescope of the claims, for the particular device, selected to illustratethe invention, is but one of many possible concrete embodiments of thesame. It is not, therefore, to be restricted to the precise details ofthe struc ture shown and described.

What I claim is:

1. In a balance, a movable member, a stationary frame, a plurality offlexing supporting elements supporting said member for movement on saidframe, an armature composed preferably of low hysteresis magneticmaterial connected to said member, spaced stationary magnetic polesmounted on opposite sides of said armature, said poles exerting opposingforces on said armature, means for adjusting said poles relative to saidarmature so that the differential of the opposing forces issubstantially equal to and opposed to the total force exerted by saidflexing supporting elements on said moving member over the operatingrange of its movement.

2. In a weighing apparatus, a base, a balance mounted on said base,flexure pivots supporting said balance, magnetic means for neutralizingthe return torque exerted by said fiexure pivots, said means comp-risingspaced magnets, and an armature associated with said balance locatedbetween said magnets, a coil mounted on said balance, a magnet providinga substantially constant uniform magnetic field in which said coilmoves, means for supplying a varying current to said coil proportionalto variations in deflecting forces applied to said balance, means forimposing a second current component in said coil to create a force whichis opposed to the movement of said balance and proportional to itsvelocity, a condenser, means for charging said condenser with a voltagesubstantially proportional to the current in said coil, means fordisconnecting said condenser from said charging means, and means formeasuring said charge after said condenser is disconnected from saidcharging means.

3. In a weighing apparatus, a base, a balance mounted on said base,flexure pivots supporting said balance, magnetic means for neutralizingthe return torque exerted by said fiexure pivots, said means comprisingspaced magnets, and an armature carried by said balance located betweensaid magnets.

4. In a weighing apparatus, a base, a balance mounted on said base,flexure pivots supporting said balance, magnetic means for neutralizingthe return torque exerted by said fiexure pivots, said means comprisingspaced magnets, and an armature associated with said balance locatedbetween said magnets, a coil mounted on said balance, a magnet providinga substantially constant uniform magnetic field in which said coilmoves, and means for supplying a varying current to said coilproportional to variations in deflecting forces applied to said balance.

5. In a weighing apparatus, a base, a balance mounted on said base,flexure pivots supporting said balance, magnetic means for neutralizingthe return torque exerted by said ilexure pivots, said means comprisingspaced magnets, and an armature associated with said balance locatedbetween said magnets, a coil mounted on said balance, a magnet providinga substantially constant uniform magnetic field in which said coilmoves, means for supplying a varying current to said coil proportionalto variations in deflecting forces applied to said balance, and meansfor imposing a second current component in said coil to create a forcewhich is opposed to the movement of said balance, and proportional toits velocity.

6. In a weighing apparatus, a base, a plurality of sets of flexiblesprings mounted in vertical spaced relationship on said base, twovertical rods carried by said springs, one of said rods being providedat one end with a coil, a magnetic field surrounding said coil; theother of said rods being spaced from said first-named rod, an armaturesecured to said second-named rod, spaced magnets mounted on oppositesides of said armature, a scale beam, means for supporting said beambetween said rods for substantially pivotal movement, means forbalancing said beam at a neutral position, an article supportoperatively connected to said second-named rod, an electric circuit,means operated by the imposition of a force on said support for causinga current to flow in said circuit and said coil of such magnitude andpolarity that the force exerted by said '15 magnetic'field on said coilas a result of said current is substantially proportional to thevelocity of movement of said beam and opposite in direction to saidmovement, and means for counterbalancing the force on said support dueto the weight of an article placed thereon.

7. In an electromagnetic weighing apparatus, a balance, means forsupplying a substantially constant uniform magnetic field, a coilattached to said balance and suspended in said field, means for varyingthe current in said coil substantially in accordance with any change inforce on said balance, a condenser, means for charging said condenserwith a voltage substantially proportional to the current in said coil,means for disconnecting said condenser from said charging means, andmeans for measuring said charge after said condenser is disconnectedfrom said charging means.

8. In an electromagnetic weighing apparatus,

a balance, means for supplying a substantially constant uniform magneticfield, a coil attached to said balance and suspended in said field,means for varying the current in said coil substantially in accordancewith any change in force on said balance, a condenser, means forcharging said condenser with a voltage substantially proportional to thecurrent in said coil, means for disconnecting said condenser from saidcharging means, a scale pan operatively associated with said balance,means for feeding a succession of articles to be weighed onto said scalepan, means for removing weighed articles from said scale pan, and meansoperated by the charge on said condenser for selectively recording theweight of each article weighed in relation to a predetermined standardweight.

9. In an electromagnetic weighing apparatus, a balance, means forsupplying a substantially constant uniform magnetic field, a coilattached to said balance and suspended in said field, means for varyingthe current in said coil in accordance with any change in weight on saidbalance, a scale pan operatively associated with said balance, means forfeeding a succession of articles to be weighed onto said scale pan,means for removing weighed articles from said scale pan, means forrecording the current flowing in said coil for each article weighed inrelation to the current for a predetermined standard weight, saidlastnamed means including a plurality of counters, an electromagnetassociated with each of said counters, and selectively operated meanscontrolled by the current in said coil for each article weighed forenergizing a selected electromagnet and its counter.

10. In an electromagnetic weighing apparatus, a balance, means forsupplying a substantially constant uniform magnetic field, a coilattached to said balance and suspended in said field, means for varyingthe current in said coil in accordance with any change in weight on saidbalance, a condenser, means for charging said condenser with a voltageproportional to the current in said coil, means for disconnecting saidcondenser from said charging means, a scale pan operatively associatedwith said balance, means for feeding a succession of articles to beweighed onto said scale pan, means for removing weighed articles fromsaid scale pan, means for selectively recording the weight of eacharticle weighed in relation to a predetermined standard weight, saidlast-named means including counters, electromagnets associated with eachof said counters, and selectively operated means controlled by thecharge of said 16 condenser for energizing a selected electromagnet andits counter.

11. In an electromagnetic balance, a stationary frame, a memberpivotally supported on said frame, a force receiving surface operativelyconnected to said member, a magnet mounted on said frame, meanspositioning said member at a neutral position, said magnet beingconstructed and arranged to maintain a constant magnetic flux in an airgap, a coil mounted on said member for movement in said air gap in adirection at right angles to said fiux, a plate mounted on said memberfor movement therewith, a stationary plate, an electric circuitassociated with said coil and said plates, means responsive to theapplication of a force to said surface for causing a current to flow insaid circuit of such magnitude and polarity that the force exerted bysaid magnetic field on said coil as a result of said current issubstantially proportional to the displacement of said m mber from saidneutral position and in a direction opposite to said displacement.

12. In an electromagnetic balance, a stationary frame, a memberp-ivotally supported on said frame, a force receiving surfaceoperatively connected to said member, a magnet mounted on said frame,means positioning said member at a neutral position, said magnet beingconstructed and arranged to maintain a constant magnetic flux in an airgap, a coil mounted on said member for movement in said air gap in adirection at right angles to said flux, a plate mounted on said memberfor movement therewith, a stationary plate, an electric circuitassociated with said coil and said plates, means responsive to theapplication of a force to said surface for causing a current to fiow insaid circuit of such magnitude and polarity that the force exerted bysaid magnetic field on said coil as a result of said current can alwaysbe resolved into two components, one of which is substantiallyproportional to the displacement of said member from said neutralposition and in opposite directions to said displacement, the othercomponent of said force being substantially proportional to the velocityof movement of said member and opposite in direction to said movement.

13. In anelectromagnetic balance, a stationary frame, a member pivotallysupported on said frame, a force receiving surface operatively connectedto said member, a magnet mounted on said frame, means positioning saidmember at a neutral position, said magnet being constructed and arrangedto maintain a constant magnetic flux in an air gap, a coil mounted onsaid member for movement in said air gap in a direction at right anglesto said flux, a plate mounted on said member for movement therewith, astationary plate, an electric circuit associated with said coil and saidplates, means responsive to the application of a force to said surfacefor causing a current to flow in said circuit of such magnitude andpolarity that the force exerted by said magnetic field on said coil as aresult of said current can always be resolved into two components, oneof which is substantially proportional to the displacement of saidmember from said neutral position and in opposite directions to saiddisplacement, the other component of said force being substantiallyproportional to the velocity of movement of said member and opposite indirection to said movement, a condenser, means for charging saidcondenser with a voltage substantially proportional to the current insaid coil, means 17 for disconnecting said condenser from said chargingmeans, and means for measuring said charge after said condenser isdisconnected from said charging means.

14. In a Weighing apparatus, a base, a plurality of flexible springsmounted on said base, a scale beam pivotally supported by said springs,a coil supported by said beam, a magnetic field surrounding said coil,an armature also supported by said beam, spaced magnets mounted onopposite sides of said armature, means for adjusting the position ofsaid magnets relative to said armature to so position said magnets thatthe combined forces exerted by said magnets on said armaturecounterbalance the forces exerted by said springs on said beam over alimited range of movement of said beam, a force-receiving surfacesupported by said beam for movement therewith, an electric circuit,means for inducing a current in said circuit and said coil of amagnitude to create a force operative to constantly balance any changein force imposed on said surface, and means for inducing a secondcurrent component in said coil to create a force operative to oppose themotion of said coil in said field.

WILLIAM C. BROEKI-IUYSEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

